1. Field of the Invention
The present invention relates to a gate valve for gas flow control in vacuum systems.
More particularly it relates to a pendulum vacuum gate valve having a first axis of motion for moving the valve plate assembly into and out of a gas flow conduit for large scale flow control throttling and a second axis of motion for fine scale flow control throttling and sealing the valve plate assembly in the passageway.
Specifically the present invention relates to a motor driven pendulum gate valve for vacuum systems which is actuated in a first axis of rotational motion of the valve assembly transverse to the gas flow to control relatively large scale volume gas flow in the system. The valve assembly is actuated in a second axis of motion longitudinal to the gas flow by air pressure to throttle comparatively fine scale volume gas flow and to alternatively seal both sides of the valve plate assembly from within the housing whereby both actuating mechanisms are sealed and separated from the vacuum chamber environment.
2. Description of the Prior Art
The use of gate valves in one form or another for the purpose of controlling gas flow in vacuum systems and lines is known in the prior art. However, despite the numerous designs, structures, forms, and variety of apparatus disclosed by and utilized in the prior art, and which have been developed for the accomplishment of the specific objectives, purposes, and requirements of gas flow control in vacuum environments, the devices, machines, and constructions which have been hereto-fore devised and utilized to accomplish these goals consist basically of familiar, expected, and obvious configurations, combinations, and arrangements, of well known structural forms and apparatus. This will become apparent from the following consideration of the the closest known and relevant prior art.
In thin film processing, as the size of the silicon wafer increases and the geometry of the device decreases, there is an ever greater need for uniform pressure and flow control in a wafer process chamber. Pendulum valves are often used to control flow/pressure in vacuum chambers and are typically located between a chamber and the vacuum pump. In these pendulum valves, the valve plate can typically move from a fully open to a fully closed position. This generally involves rotating a valve plate assembly transversely from an open position in the gas flow channel to an interposed condition and then moving the seal plates vertically, or longitudinally within the channel, to the closed position to seal the valve.
Prior art pendulum valves typically use a rotating shaft to swing the valve plate assembly between open and closed positions. Usually a secondary mechanism which uses air cylinders, cams, or linkage converts horizontal motion into vertical movement of the valve plate assembly to make a tight seal. These prior art mechanisms are complex and relatively dirty for use in vacuum chamber conditions and create maintenance problems. The actuation mechanisms are usually exposed to the gas flow inside the valve housing and are a common source for contaminant origination in a vacuum environment. Wear and rubbing of the operative parts of the valve generate the contaminants to the vacuum environment reducing yield and causing prolonged maintenance downtime.
In situations where valves operate under heated conditions, the reliability of mechanical linkages is further reduced. The pendulum vacuum gate valve contemplated according to the present invention has no linkages, no rubbing or wearing surfaces, and this allows high-temperature bake with no adverse effects. The present invention departs substantially from the conventional concepts and designs used by the prior art, and in doing so, provides an apparatus primarily developed for the purpose of overcoming the problems as described above. However, it accomplishes the result in a different manner with an optimally designed apparatus for producing an improved pendulum vacuum gate valve which is more effective, cleaner, more reliable, and bakeable (can be subjected to high temperature heating).